The phospholipid content of, and asymmetry in the erythrocyte membrane is employed as a guide to select certain binary and ternary lipid mixtures for NMR investigations. The lipids in these systems will consist of phosphatidyl choline, ethanolamine, serine, sphingo myelin and/or cholesterol. In each case, one molecule will, by chemical syntheses be 2H labeled in either the fatty acyl or sphingosine chains, glycerol backbone, or head groups. We plan to examine the alterations in their 2H NMR spectra brought about by the presence of a second and/or third lipid molecule. Because of the unique capabilities of our NMR spectrometer, the experiments will be performed both above and below the gel-liquid crystalline transition temperature. The studies should elucidate the molecular details of the phase transition mechanisms in pure and mixed systems and also permit an assessment of the manner in which a number of factors effect membrane structure. These are: Changes in head groups or degree of acyl chain unsaturation, introduction of the ceramide moiety, and pH and divalent cations. Completion of this work will permit quantitative study of lipid mixtures which are close facsimiles of biological membranes.